1. Field of the Invention
The invention relates to semi-trailer subframes, and in particular to movable subframes for a semi-trailer. More particularly, the invention is directed to a movable subframe for a semi-trailer which accommodates storage of a walk ramp beneath the semi-trailer.
2. Background Art
Movable subframes, typically referred to as sliders, have been utilized on semi-trailers or tractor-trailers for many years. One or more axle/suspension systems usually are suspended from a single slider structure. The slider in turn is mounted on the underside of the trailer body, and is movable longitudinally therealong to provide a means of variable load distribution. More specifically, the amount of cargo that a trailer may carry is governed by local, state and/or national road and bridge laws, and is dependent on proper load distribution. The basic principle behind most road and bridge laws is to limit the maximum load that a vehicle may carry, as well as to limit the maximum load that can be supported by individual axles. A trailer having a slider gains an advantage with respect to laws governing maximum axle loads. More particularly, proper placement of the slider varies individual axle loads or redistributes the trailer load so that it is within legal limits.
Once properly positioned, the slider is locked in place on the underside of the trailer by a retractable pin mechanism. The retractable pin mechanism generally includes two or more, and typically four, retractable pins which may be interconnected by a usually manually or pneumatically actuated crank mechanism. When the pins are in their extended or outboardmost position, they each extend through a respective opening formed in the slider and into a selected aligned one of a plurality of openings formed in rails depending from the trailer body. The pins thereby lock the slider in a selected position relative to the trailer body.
However, known prior art sliders fail to provide for incorporation of a storable walk ramp beneath the trailer. Such walk ramps typically are required on trailers used in food service and appliance delivery applications, as well as in other applications. Since known prior art sliders are not made to accommodate storage of a walk ramp, if a ramp must be installed on a trailer having a prior art slider, a pair of large steel spacers usually is attached to the bottom of the trailer and extends the full length of the body rails, which is typically about 200 to 300 inches. The spacers are needed to provide clearance for the walk ramp carrier, which has a cross-section of approximately 6 inches high by 28 inches wide and is mounted on the underside of the trailer. The trailer body rails then can be attached to the bottom of the spacers, instead of the bottom of the trailer, and the slider in turn is mounted on the rails in the usual manner. Unfortunately, while such an arrangement of parts accommodates storage of the walk ramp when not in use and its carrier, the prior art spacer system adds significant unwanted weight to the semi-trailer.
The present invention solves the above-described weight problem in the following manner. Rather than attaching spacers the entire length of the trailer body rails, a spacer cap is attached directly to each main member of the slider and measures only about 96 inches in length, thus saving significant weight over the above-described prior art arrangement of parts. The slider locking pins are relocated into the spacer caps to allow standard trailer body rails to be utilized. The present invention can be utilized in new trailer manufacturing, as well as on existing trailers of semi-trailers using prior art sliders, to easily convert such existing trailers to accommodate walk ramp storage merely by replacing the prior art slider with the slider of the present invention. This ease of conversion should be compared to the case where it is desired to utilize the prior art walk ramp storage spacer system, which would require that the rails be cut off the trailer body, the spacers installed, and the rails reattached.